For the preparation of highly isotactic polyolefins by means of stereospecific racemic metallocene/cocatalyst systems, the highest possible isotacticity is desired. This means that very stereoselective racemic metallocene types are employed which are able to build up polymer chains having very few construction faults. The consequence of this is that products having high crystallinity, high melting point and thus also high hardness and excellent modules of elasticity in flexing are obtained as desired.
However, it is disadvantageous that these polymers are difficult to process, and in particular problems occur during extrusion, injection molding and thermoforming. Admixing of flow improvers and other modifying components could help here, but results in the good product properties, such as, for example, the high hardness, being drastically reduced. In addition, tackiness and fogging also occur. The object was thus to improve the processing properties of highly isotactic polyolefins of this type without in this way impairing the good properties of the moldings produced therefrom.
Surprisingly, we have found that it rac/meso mixtures of certain metallocenes are used, the processing problems can be eliminated without the abovementioned good product properties being lost.
In addition, the use of these specific metallocenes in their pure meso-form makes it possible to prepare high-molecular-weight atactic polyolefins which can be homogeneously admixed, as additives, with other polyolefins.
This was not possible with the low-molecular weight polyolefins accessible hitherto due to the large differences in viscosity between the polyolefin matrix and the atactic component.
Such admixtures improve polyolefin moldings with respect to their surface gloss, their impact strength and their transparency. In addition, the processing properties of such polyolefins are likewise improved by admixing the high-molecular-weight atactic polyolefin. Likewise, tackiness and fogging do not occur.
Homogeneous miscibility of the atactic component is so important because only with a homogeneous material can a usable molding with a good surface and long service life be produced and only in the case of homogeneous distribution do the qualities of the atactic component come out in full.
The invention thus relates to the preparation of polyolefins which
1) are atactic, i.e. have an isotactic index of xe2x89xa660%, and are high-molecular, i.e. have a viscosity index of  greater than 80 cm3/g and a molecular weight Mw of  greater than 100,000 g/mol with a polydispersity Mw/Mn of xe2x89xa64.0, or
2) comprise at least two types of polyolefin chains, namely
a) a maximum of 99% by weight, preferably a maximum of 98% by weight, of the polymer chains in the polyolefin as a whole comprise xcex1-olefin units linked in a highly isotactic manner, with an isotactic index of  greater than 90% and a polydispersity of xe2x89xa64.0, and
b) at least 1% by weight, preferably at least 2% by weight, of the polymer chains in the polyolefin as a whole comprise atactic polyolefins of the type described under 1).
Polyolefins which conform to the description under 2) can either be prepared directly in the polymerization or are prepared by melt-mixing in an extruder or compounder.
The invention thus relates to a process for the preparation of an olefin polymer by polymerization or copolymerization of an olefin of the formula Raxe2x80x94CHxe2x95x90CHxe2x80x94Rb, in which Ra and Rb are identical or different and are a hydrogen atom or a hydrocarbon radical having 1 to 14 carbon atoms, or Ra and Rb, together with the atoms connecting them, can form a ring, at a temperature of from xe2x88x9260 to 200xc2x0 C., at a pressure of from 0.5 to 100 bar, in solution, in suspension or in the gas phase, in the presence of a catalyst formed from a metallocene as transition-metal compound and a cocatalyst, wherein the metallocene is a compound of the formula I which is used in the pure meso-form for the preparation of polyolefins of type 1 and used in a meso:rac ratio of greater than 1:99, preferably greater than 2:98, for the preparation of type 2 polyolefins, 
in which
M1 is a metal from group IVb, Vb or VIb of the Periodic Table,
R1 and R2 are identical or different and are a hydrogen atom, a C1-C10-alkyl group, a C1-C10-alkoxy group, a C6-C10-aryl group, a C6-C10-aryloxy group, a C2-C10-alkenyl group, a C7-C40-arylalkyl group, a C7-C40-alkylaryl group, at C8-C40-arylalkenyl group, or a halogen atom,
the radicals R4 and R5 are identical or different and are a hydrogen atom, a halogen atom, a C1-C10-alkyl group, which may be halogenated, a C6-C10-aryl group, which may be halogenated, and an xe2x80x94NR102, xe2x80x94SR10, xe2x80x94OSiR103, xe2x80x94SiR103 or xe2x80x94PR102 radical in which R10 is a halogen atom, a C1-C10-alkyl group or a C6-C10aryl group,
R3 and R6 are identical or different and are as defined as for R4, with the proviso that R3 and R6 are not hydrogen,
or two or more of the radicals R3 to R6, together with the atoms connecting them, form a ring system, 
xe2x95x90BR11, xe2x95x90AlR11, xe2x80x94Gexe2x80x94, xe2x80x94Snxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90SO, xe2x95x90SO2, xe2x95x90NR11, xe2x95x90CO, xe2x95x90PR11 or xe2x95x90P(O)R11, where
R11, R12 and R13 are identical or different and are a hydrogen atom, a halogen atom, a C1-C10-alkyl group, a C1-C10-fluoroalkyl group, a C6-C10-aryl group, a C6-C10-fluoroaryl group, a C1-C10-alkoxy group, a C2-C10-alkenyl group, a C7-C40-arylalkyl group, a C8-C40-arylalkenyl group or a C7-C40-alkylaryl group, or R11 and R12 or R11 and R13, in each case together with the atoms connecting them, form a ring,
M2 is silicon, germanium or tin,
R8 and R9 are identical or different and are as defined for R11, and
m and n are identical or different and are zero, 1 or 2, where m plus n is zero, 1 or 2.
Alkyl is straight-chain or branched alkyl. Halogen (halogenated) means fluorine, chlorine, bromine or iodine, preferably fluorine or chlorine.
The substitutents R3, R4, R5 and R6 may be different in spite of the same indexing.
The catalyst to be used for the process according to the invention comprises a cocatalyst and a metallocene of the formula I.
In the formula I, M1 is a metal from group IVb, Vb or VIb of the Periodic Table, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten, preferably zirconium, hafnium or titanium.
R1 and R2 are identical or different and are a hydrogen atom, a C1-C10-, preferably C1-C3-alkyl group, a C1-C10-, preferably C1-C3-alkoxy group, a C4-C10-, preferably C6-C8-aryl group, a C6-C10-, preferably C4-C8-aryloxy group, a C2-C10-, preferably C2-C6-alkenyl group, a C7-C40-, preferably C7-C10-arylalkyl group, a C7-C40-, preferably a C7-C12-alkylaryl group, a C8-C40-, preferably a C8-C12-aryalkenyl group, or a halogen atom, preferably chlorine.
The radicals R4 and R5 are identical or different and are a hydrogen atom, a halogen atom, preferably a fluorine, chlorine or bromine atom, a C1-C10-, preferably C1-C4-alkyl group, which may be halogenated, a C6-C10-, preferably a C6-C9-aryl group, which may be halogenated, an xe2x80x94NR102, xe2x80x94SR10, xe2x80x94OSiR103, xe2x80x94SiR103 or xe2x95x90PR102 radical, in which R10 is a halogen atom, preferably a chlorine atom, or a C1-C10-, preferably a C1-C3-alkyl group, or a C6-C10- preferably C6-C8-aryl group. R4 and R5 are particularly preferably hydrogen, C1-C4-alkyl or C6-C9-aryl.
R3 and R6 are identical or different and are defined for R4, with the proviso that R3 and R6 must not be hydrogen. R3 and R6 are preferably (C1-C4)-alkyl or C6-C9-aryl, both of which may be halogenated, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, trifluoromethyl, phenyl, tolyl or mesityl, in particular methyl, isopropyl or phenyl.
Two or more of the radicals R3 to R6 may alternatively, together with the atoms connecting them, form an aromatic or aliphatic ring system. Adjacent radicals, in particular R4 and R6, together preferably form a ring. 
xe2x95x90BR11, xe2x95x90AlR11, xe2x80x94Gexe2x80x94, xe2x80x94Snxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90SO, xe2x95x90SO2, xe2x95x90NR11, xe2x95x90CO, xe2x95x90PR11 or xe2x95x90P(O)R11, where R11, R12 and R13 are identical or different and are a hydrogen atom, a halogen atom, a C1-C10-, preferably C1-C4-alkyl group, in particular a methyl group, a C2-C10-fluoroalkyl group, preferably a CF3 group, a C6-C10-, preferably C6-C8-aryl group, a C6-C10-fluoroaryl group, preferably a pentafluorophenyl group, a C1-C10-, preferably a C1-C4-alkoxy group, in particular a methoxy group, a C2-C10-, preferably C2-C4-alkenyl group, a C7-C40-, preferably C7-C10-arylalkyl group, a C8-C40-, preferably C8-C12-arylalkenyl group or a C7-C40-, preferably C7-C12-alkylaryl group, or R11 and R12 or R11 and R13, in each case together with the atoms connecting them, form a ring.
M2 is silicon, germanium or tin, preferably silicon or germanium.
R7 is preferably xe2x95x90CR11R12, xe2x95x90SiR11R12, xe2x95x90GeR11R12, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x95x90SO, xe2x95x90PR11 or xe2x95x90P(O)R11.
R8 and R9 are identical or different and are as defined for R11.
m and n are identical or different and are zero, 1 or 2, preferably zero or 1, where m plus n is zero, 1 or 2, preferably zero or 1.
Particularly preferred metallocenes are thus the compounds of the formulae A and B 
where
M1 is Zr or Ef; R1 and R2 are methyl or chlorine; R3 and R6 are methyl, isopropyl, phenyl, ethyl or trifluoromethyl;
R4 and R5 are hydrogen or as defined for R3 and R6, or R4 can form an aliphatic or aromatic ring with R6; the same also applies to adjacent radicals R4; and R8, R9, R11 and
R12 are as defined above, in particular the compounds I listed in the working examples.
This means that the indenyl radicals of the compounds I are substituted, in particular, in the 2,4-position, in the 2,4,6-position, in the 2,4,5-position or in the 2,4,5,6-position, and the radicals in the 3- and 7-positions are preferably hydrogen.
Nomenclature 
The metallocenes described above can be prepared by the following reaction scheme, which is known from the literature: 
The compounds are formed from the synthesis as rac/meso mixtures. The meso or rac form can be increased in concentration by fractional crystallization, for example in a hydrocarbon. This procedure is known and is part of the prior art.
The cocatalyst used according to the invention is preferably an aluminoxane of the formula (II) 
for the linear type and/or of the formula (III) 
for the cyclic type, where, in the formulae (II) and (III), the radicals R14 may be identical or different and are a C1-C6-alkyl group, a C6-C18-aryl group, benzyl or hydrogen, and p is an integer from 2 to 50, preferably from 10 to 35.
The radicals R14 are preferably identical and are preferably methyl, isobutyl, phenyl or benzyl, particularly preferably methyl.
If the radicals R14 are different, they are preferably methyl and hydrogen or alternatively methyl and isobutyl, where hydrogen and isobutyl are preferably present to the extent of 0.01-40% (number of radicals R14).
The aluminoxane can be prepared in various ways by known processes. One of the methods is, for example, to react an aluminum hydrocarbon compound and/or a hydridoaluminum hydrocarbon compound with water (in gas, solid, liquid or bonded formxe2x80x94for example as water of crystallization) in an inert solvent (such as, for example, toluene). In order to prepare an aluminoxane containing different alkyl groups R14 two different trialkylaluminum compounds (AlR3+AlRxe2x80x23) corresponding to the desired composition are reacted with water (cf. S. Pasynkiewicz, Polyhedron 9 (1990) 429 and EP-A 302 424).
The precise structure of the aluminoxanes II and III is unknown.
Regardless of the preparation method, all the aluminoxane solutions have in common a varying content of unreacted aluminum starting compound, in free form or as an adduct.
It is possible to preactivate the metallocene by means of an aluminoxane of the formula (II) and/or (III) before use in the polymerization reaction. This significantly increases the polymerization activity and improves the grain morphology.
The preactivation of the transition-metal compound is carried out in solution. The metallocene is preferably dissolved in a solution of the aluminoxane in an inert hydrocarbon. Suitable inert hydrocarbons are aliphatic and aromatic hydrocarbons. Toluene is preferably used.
The concentration of the aluminoxane in the solution is in the range from about 1% by weight to the saturation limit, preferably from 5 to 30% by weight, in each case based on the solution as a whole. The metallocene can be employed in the same concentration, but is preferably employed in an amount of from 10xe2x88x924 to 1 mol per mol of aluminoxane. The preactivation time is from 5 minutes to 60 hours, preferably from 5 to 60 minutes. The reaction is carried out at a temperature of from xe2x88x9278xc2x0 C. to 100xc2x0 C., preferably from 0 to 70xc2x0 C.
The metallocene can also be prepolymerized or applied to a support. Prepolymerization is preferably carried out using the (or one of the) olefin(s) employed in the polymerization.
Examples of suitable supports are silica gels, aluminum oxides, solid aluminoxane or other inorganic support materials. Another suitable support material is a polyolefin powder in finely divided form.
According to the invention, compounds of the formulae RxNH4xe2x88x92xBRxe2x80x24, RxPH4xe2x88x92xBRxe2x80x24, R3CBRxe2x80x24 or BRxe2x80x23 can be used as suitable cocatalysts instead of or in addition to an aluminoxane. In these formulae, x is a number from 1 to 4, preferably 3, the radicals R are identical or different, preferably identical, and are C1-C10-alkyl, or C6-C18-aryl or 2 radicals R, together with the atom connecting them, form a ring, and the radicals Rxe2x80x2 are identical or different, preferably identical, and are C6-C18-aryl, which may be substituted by alkyl, haloalkyl or fluorine.
In particular, R is ethyl, propyl, butyl or phenyl, and Rxe2x80x2 is phenyl, pentafluorophenyl, 3,5-bistrifluoromethyl-phenyl, mesityl, xylyl or tolyl (cf. EP-A 277 003, EP-A 277 004 and EP-A 426 638).
When the abovementioned cocatalysts are used, the actual (active) polymerization catalyst comprises the product of the reaction of the metallocene and one of said compounds. For this reason, this reaction product is preferably prepared first outside the polymerization reactor in a separate step using a suitable solvent.
In principle, suitable cocatalysts are according to the invention any compounds which, due to their Lewis acidity, are able to convert the neutral metallocene into a cation and stabilize the latter (xe2x80x9clabile coordinationxe2x80x9d). In addition, the cocatalyst or the anion formed therefrom should not undergo any further reactions with the metallocene cation formed (cf. EP-A 427 697).
In order to remove catalyst poisons present in the olefin, purification by means of an alkylaluminum compound, for example Alme3 or AlEt3, is advantageous. This purification can be carried out either in the polymerization system itself, or the olefin is brought into contact with the Al compound before addition to the polymerization system and is subsequently separated off again.
The polymerization or copolymerization is carried out in known manner in solution, in suspension or in the gas phase, continuously or batchwise, in one or more steps, at a temperature of from xe2x88x9260 to 200xc2x0 C., preferably from 30 to 80xc2x0 C., particularly preferably at from 50 to 80xc2x0 C. The polymerization or copolymerization is carried out using olefins of the formula Raxe2x80x94CHxe2x95x90CHxe2x80x94Rb. In this formula, Ra and Rb are identical or different and are a hydrogen atom or an alkyl radical having 1 to 14 carbon atoms. However, Ra and Rb, together with the carbon atoms connecting them, may alternatively form a ring. Examples of such olefins are ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, norbornene and norbonadiene. In particular, propylene and ethylene are polymerized.
If necessary, hydrogen is added as molecular weight regulator and/or to increase the activity. The overall pressure in the polymerization system is 0.5 to 100 bar. The polymerization is preferably carried out in the industrially particularly relevant pressure range of from 5 to 64 bar.
The metallocene is used in a concentration, based on the transition metal, of from 10xe2x88x923 to 10xe2x88x928 mol, preferably from 10xe2x88x924 to 10xe2x88x927 mol, of transition metal per dm3 of solvent or per dm3 of reactor volume. The aluminoxane is used in a concentration of from 10xe2x88x925 to 10xe2x88x921 mol, preferably from 10xe2x88x924 to 10xe2x88x922 mol, per dm3 of solvent or per dm3 of reactor volume. The other cocatalysts mentioned are used in approximately equimolar amounts with respect to the metallocene. In principle, however, higher concentrations are also possible.
If the polymerization is carried out as a suspension or solution polymerization, an inert solvent which is customary for the Ziegler low-pressure process is used. For example, the process is carried out in an aliphatic or cycloaliphatic hydrocarbon; examples of such hydrocarbons which may be mentioned are propane, butane, pentane, hexane, heptane, isooctane, cyclohexane and methylcyclohexane.
It is also possible to use a benzine or hydrogenated diesel oil fraction. Toluene can also be used. The polymerization is preferably carried out in the liquid monomer.
If inert solvents are used, the monomers are metered in as gases or liquids.
The polymerization can have any desired duration, since the catalyst system to be used according to the invention only exhibits a slight drop in polymerization activity as a function of time.
The process according to the invention is distinguished by the fact that the meso-metallocenes described give atactic polymers of high molecular weight in the industrially particularly relevant temperature range between 50 and 80xc2x0 C. rac/meso mixtures of the metallocenes according to the invention give homogeneous polymers with particular good processing properties. Moldings produced therefrom are distinguished by good surfaces and high transparency. In addition, high surface hardnesses and good moduli of elasticity in flexing are characteristics of these moldings.
The high-molecular-weight atactic component is not tacky, and the moldings are furthemore distinguished by very good fogging behavior.